Our species caused 322 animal extinctions over the past 500 years, with two-thirds of those occurring in the last two centuries, according to a paper published in a special issue of the journal Science this week.

Top image: Black rhino. Last year, one if its subspecies, the Western Black Rhino, was officially declared extinct, the result of excessive poaching Image: John & Karen Hollingsworth, Wikimedia Commons.

Many animals are threatened with human-caused extinction now, with researchers expressing particular concern over amphibian and invertebrate (creatures without a backbone) losses. Numbers of the latter group have nearly halved as our population doubled in size over the past 35 years.

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Ecologists, zoologists and other scientists believe that without urgent steps to stem the losses, we are facing global scale tipping points from which we may never look back or recover.

Decreasing Footprints

"Indeed, if current rates (of human population growth) were to continue unchecked, population size would be, by 2100, about 27 billion persons — clearly an unthinkable and unsustainable option," co-author Rodolfo Dirzo, professor of environmental sciences at Stanford University, told Discovery News.

Dirzo and his colleagues call for "decreasing the per capita human footprint," by developing and implementing carbon-neutral technologies, producing food and goods more efficiently, consuming less and wasting less.

They also say it is essential we ensure that lower human population growth projections are the "ones that prevail."

Worth More Alive Than Dead

Haldre Rogers and Josh Tewksbury, authors of another paper in the same issue, believe that, "animals do matter to people, but on balance, they matter less than food, jobs, energy, money, and development."

They continued, "As long as we continue to view animals in ecosystems as irrelevant to these basic demands, animals will lose."

Keeping animals alive and ecosystems healthy translate to big bucks on a global scale. Tewksbury, director of the Luc Hoffmann Institute of the World Wide Fund for Nature, pointed out that Southeast Asia's Mekong River Basin supports 60 million people through its fisheries. Rogers, a researcher in Rice University's Department of Ecology & Evolutionary Biology, added that 7% of visitors to Namibia are nature-based tourists, with their money accounting for 14.2% of that nation's economic growth.

"Whale watching in Latin America alone generates over 275 million dollars a year," Tewksbury said. "Multiple studies have demonstrated how turtles are worth more alive than dead."

In the United States, he added, shark-watching results in $314 million per year, directly supporting 10,000 jobs.

He and the other researchers point out that human health, pollination, pest control, water quality, food availability and other critical factors are also dependent on ecosystem stability.

In the United States, he added, shark-watching results in $314 million per year, directly supporting 10,000 jobs.

He and the other researchers say that human health, pollination, pest control, water quality, food availability and other critical factors are also dependent upon ecosystem stability.

Enacting Measures

Yet another paper in the latest issue of Science outlines controversial measures to improve the current situation beyond basic conservation efforts. These include re-wilding, meaning placement of underrepresented species back into the wild; human removal of invasive species; and, perhaps most controversial of all, de-extinction: bringing already extinct species back to life.

"People are currently grappling with the implications of de-extinction, including how to select the best candidate species," co-author Philip Seddon, a zoologist at the University of Otago, told Discovery News.

Rogers said that restoration and re-introduction have shown progress.

"The return of the bald eagle and the California condor to the skies and the wild turkey to the lands of the U.S. are great success stories," she said.

She and Tewksbury are also working on the island of Guam, where the invasive brown tree snake has rid the island of birds, causing the forests there to be without seed dispersers for 30 years. This, in turn, has contributed to financial challenges for locals.

It's a mistake, though, to limit the value of non-human animals to their economic value, the researchers believe.

"From the cave paintings that represent the dawn of art to the icons of culture and sport around the world today, wild animals are a part of our fabric, and in a very real, evolutionary sense, these animals have made us who we are," said Tewksbury.

"The loss of these animals from landscapes around the world is thus a loss for all of humanity."